Breeding of an elite cultivar Haibao No. 1 of Undaria pinnatifida (Phaeophyceae) through gametophyte clone crossing and consecutive selection

As a commercially important kelp, Undaria pinnatifida has been farmed in northern China for more than 30 years. Farming of U. pinnatifida has been restrained historically by the lack of cultivars ever since the very beginning of its cultivation. The cultivation industry to a large extent relies on introducing seedlings or parental plants from other East Asian countries from time to time due to the degeneration of the sporophytes. In order to change this awkward situation, an elite cultivar named Haibao No. 1 was developed through gametophyte clone crossing and consecutive selection. Its original parents were selected from cultivation populations in Dalian. The most pronounced agronomic characteristic of this novel cultivar was its high yield. From F2 to F5, the average fresh weight per individual was all significantly higher than the control. In large-scale cultivation of F4 and F5 populations, the fresh weight reached 19–20 kg m−1 on cultivation line, increasing the yield by more than 40 %. F4 population of the cultivar showed significant heterozygosity deficiency (F is = 0.4728) as revealed by the microsatellite analysis at 20 loci, suggesting the effect of consecutive inbreeding. Coefficients of variations (CVs) of the blade width, the width of the undivided part of the blade, the stipe width, and the fresh weight ranged from 12.82 to 22.3 %, which seemed to be high; however, when compared with the crossing line derived from the crossing of a pair of male and female gametophyte clones, the CVs were close between them, which implied that these variations were attributed to environmental rather than genetic difference. The most suitable beginning time for harvesting of this cultivar was in middle April, when the average fresh weight per individual reached the highest value. Besides high yield, Haibao No. 1 was also characterized by possessing the wide stipe, long special-grade midrib, and large sporophylls. All these characteristics contributed to the much higher commercial value of this cultivar than the controls.